1. Field of the Invention
The present invention relates to a noise canceler for use in, e.g., a voice communication system, and capable of canceling background noise contained in an input acoustic signal and superposed on a speech signal.
2. Description of Background Art
A noise canceler for the above application is disclosed in, e.g., Masanori Akita and Takeshi Ohkura "A Method of Revising Spectral Envelopes under the Noisy Environment for Speech Processing", Technical Report of IEICE, EA95-57, November, 1995. The noise canceler includes an analog-to-digital converter (ADC). When a speech and noise derived from a speech source and a background noise source, respectively, are input to a microphone, the ADC converts them to a digital electric signal. A simple frequency or spectrum subtracting section executes Fast Fourier Transform (FFT) with the digital signal, and then executes simple frequency subtraction. A spectrum correcting section estimates and then restores valleys originally present in the speech signal input to the noise canceler, but lost in the output signal of the simple frequency subtracting section due to the limitation of low levels. In this manner, the conventional noise canceler reduces background noise by simple frequency subtraction and spectrum correction, and then restores and thereby enhances a speech spectrum. However, this kind of scheme has some problems left unsolved, as will be described specifically later.